Kate's Severe Morning Sickness Could Be Hereditary

Known as hyperemesis gravidarum (HG), the condition – for which Kate was hospitalized for four days – is characterized by debilitating nausea and vomiting that severely inhibits a woman's ability to eat or drink and results in significant weight loss. Affecting up to 2 percent of all pregnant women, it can start as early as five weeks into pregnancy and endure for weeks or even months.

The condition typically comes on suddenly. During a visit to her prep school, St. Andrew's, on Nov. 30, a seemingly upbeat Kate dined on Scottish beef and played field hockey in 3-inch heels. Just two days later, she was rushed to the hospital and her pregnancy announced.

"It's the body reaction to the pregnancy hormone," Dr. Dagni Rajasingam, spokesperson for the Royal College of Obstetricians, tells PEOPLE. "Some women who are very sensitive to it can start feeling nauseated early on in pregnancy and it will provoke them to take the test."

Treatment options include IVs for fluids and, in at least 20 percent of cases, feeding tubes for nutrition. Anti-nausea medications commonly used for chemotherapy patients are often prescribed off-label for women suffering with HG, but "it's certainly not a cure," says Dr. Marlena Fejzo, a UCLA professor of research and leading expert on HG. Nor is there extensive research examining the potential effects of such medications on women and their babies.

Although the cause is unknown, a family history of HG raises a woman's risk. Women carrying multiples are also more likely to develop HG, as are women carrying girls. "The leading theory is that the cause is hormonal," says Dr. Fejzo. "Obviously when you're carrying twins those hormones are higher, so if you have a problem processing those hormones then you're more likely to feel worse."

Among the complications of HG for the mother: post-traumatic stress resulting "from the severe, prolonged nausea at a time when you know you're supposed to give your baby nutrients and you just can't," says Dr. Fejzo, who lost a baby to HG in 1999. "It's hell for these women – like going through a war." For the baby, complications can include fetal death, an increase in pre-term birth and low-birth weight.

Dr. Fejzo and others hope that the princess's struggle will shed a light on the disease to help boost research and funding for better treatment options. "It's a horrible condition," says Sarah Rosen, a Chicago-area mom who suffered from HG during her first pregnancy, "but at least maybe this will draw some attention to it."